SGS WOOL TESTING SERVICES
2011
INFO BULLETIN VOL 1.4A
WHAT DOES STAPLE LENGTH AND STRENGTH DATA
MEAN?
INTRODUCTION
New Zealand only produces
approximately 10,000 tons of merino
wool each year, of which still only a
relatively small proportion is tested for
length & strength. However, most of
this is high quality, with good staple
length, high strength, low VM and good
style.
Typical results for NZ merino wool
are staple lengths of 60 to 95 mm,
strengths varying from 25 to 55 N/ktex,
and VMB levels of 0 to 1.3 %, but how
does one judge these results? On their
own, this is fairly difficult, because the
primary parameters that the end user is
interested in are hauteur (H), CvH and
noil (expressed as romaine), although,
as discussed in Info-bulletin 1.6,
staple strength has now become very
important on its own.
ASSESSING SL, CVL, SS
AND POB
Staple length is directly related to
combing length, and this therefore is
one of the primary specifications. The
coefficient of variation of staple length
(CvSL) gives an indication of how
uniform a lot of wool is, or, how well
prepared. Expected ranges are 10 to
20% for fleece wools and 18 to 30% for
skirtings.
80
20
60
15
40
10
20
5
0
40
Preicted Romaine %
TYPICAL RESULTS IN
NEW ZEALAND
Predicted CvHa %
Info-bulletin 1.1 describes staple length &
strength measurements in a very general
manner, and briefly mentions the use
of these measurements. This bulletin
addresses more specific questions
concerning the relationship between the
raw results of the iWTO-30 test method
and the processing performance of the
wool.
Typical TEAM CvHa and Romaine values versus Ha for NZ merinos
50
60
Predicted Ha mm
(Left) Predicted CvH %
70
0
80
(Right) Predicted Romaine %
Staple strength indicates how a wool will survive the rigours of processing. Weak
wools break easily, and consequently during carding may reduce significantly in length.
Wools can be loosely classified as follows: very tender less than 15 N/ktex; tender 20
to 30 N/ktex, sound 30 to 40 N/ktex, and very sound 45 N/Ktex and above.
Position of break appears on test certificates as the percentages of staples broken in
the tip, middle and base. Wools which have a high middle break % tend to produce
more short fibre after carding, since the fibres tend to break in the middle, and it this
figure which is used in calculating the effect on processed length.
THE TEAM PREDICTIONS
Buyers use the TEAM equations to predict the processing performance of combing
wools. Under TEAM-3 these are:
Ha = 0.43 L+0.35 S+1.38 D-0.15 M-0.45 V-0.59 CvD-0.32 CvL +21.8+MA
CvHa = 0.30 L-0.37 S-0.88 D+0.17 M+0.38 CvL+35.6+MA
Rom = -0.13 L-0.18 S-0.63 D+0.78 V+38.6+MA
SGS WOOL TESTING SERVICES
Ha is the predicted hauteur in the top,
which is approximately the average fibre
length in the top. CvHa is the predicted
coefficient of variation of Ha. Romaine
(Rom) is predicted short fibre combed
out (noil) expressed as a percentage of
total top and noil. L is staple length,
S is staple strength, D is mean fibre
diameter, V is vegetable matter base%,
CvD is coefficient of variation of fibre
diameter, CvL is coefficient of variation
of staple length, and M is % mid breaks.
MA is a mill-specific correction, which
allows for the fact that mills perform
differently to each other. The TEAM3 equation was adopted in 2006 and
removes some of the biases which
had developed with TEAM-2 due to the
improving efficiencies in mills.
From these equations it can be seen
that, for example, 10 mm increase in
staple length, would predict 4.3 mm
increase in hauteur, 3.0% increase in
CvHa, and 1.3% decrease in romaine;
whereas 10 N/ktex lower staple strength
would reduce H by 3.5 mm, increase
CvHa by 3.7%, and increase romaine by
1.8%.
INFO BULLETIN VOL 1.4A
2
OTHER PREDICTION
METHODS
For carding wools, the LAC method
(Info-bulletin 1.2) gives a prediction of
processed fibre length (as barbe rather
than hauteur) by emulating the semiworsted process in the laboratory.
Researchers in Australia are also
examining ways of predicting both
topmaking and next-to-skin wearer
performance using the diameter-length
profiles of raw wool samples (see Infobulletin 1.5). It has been suggested that
profile data better explains some aspects
of processing performance than the
TEAM equations, although more work is
needed. Research is also under way to
predict staple strength from fibre profile
data.
Whilst there has been work to show that
longer hauteur spins better, most mills
prefer to work within a band of H values
to avoid having to adjust their equipment.
Lower CvH is desirable from a spinner’s
perspective, and since noil has a low
market value, lower romaines are also
very desirable.
FOR ENQUIRIES
Email us at [email protected]
Or contact us at:
48 Kemp Street, Kilbirnie
PO Box 15062
Wellington, New Zealand
Tel:
+64.4.387.8565
Fax:
+64.4.387.8651
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